The present invention relates to a process for separating particles into three fractions of similar composition. The invention also relates to apparatus for conducting the process.
In particular, the process herein relates to the separation of an ore into three fractions consisting of a concentrate, middling and tailing. More particularly, the process relates to separating an ore into three fractions by utilizing the surface chemical properties of the ore particles to distinguish among the ore particles.
The process and apparatus have utility in the categorizing of mineral ores, such as limestone, quartz, magnesite, chalcopyrite, chalcocite, galena, sphalerite and the like, and other ore-like particles such as coal, oil shale and the like. For convenience, coal and oil shale are encompassed within the broad definition of ore as used herein.
Current methods of optically sorting a component from an ore in which it is contained utilize the natural or induced differences in color or reflectivity of the various components which constitute an ore. Using such differences in coloration or reflectivity, the components of an ore can be separated by hand or mechanical optical sorting techniques. However, some problems are presented with current optical sorting techniques.
One problem encountered in separating the components of an ore is the occurrence of a range of colors or reflectivity for a valuable component within the ore. Such a range of colors or reflectivity for the valuable component can overlap a range of colors or reflectivity exhibited by a nonvaluable component in the ore, e.g., both limestone and quartz can have essentially the same color and reflectivity. Therefore, during the separation and sorting of the components of an ore some of the nonvaluable ore components are sorted along with the valuable ore components and some of the valuable ore components are discarded with the gangue. Further, when there is an overlap of the range of color and reflectivity for the valuable and nonvaluable components, there is a sacrifice of percent yield when purity of the valuable component is desired and correspondingly there is a sacrifice of percent purity when a high yield of valuable component is desired.
A disadvantage of optically sorting components of an ore by the naturally occurring color and reflectivity of the individual components is that such a sorting method is limited to use on only those ores wherein the individual components exhibit a color or reflectivity capable of being differentiated.
Separating ore components by their naturally occurring differences in color or reflectivity is conducted by hand sorting or by machine which senses color or reflectivity. Hand sorting is limited to the ability of the individual to discern optical differences in color and/or reflectivity. Hand sorting is typically a job for unskilled labor. Due to this level of skill of the laborer and the tediousness of the job, there is generally a high turnover rate for workers involved in such hand-sorting operations. Unfortunately, the ability to separate the components of an ore by hand-sorting techniques in order to obtain products of value, is acquired either after extensive training or by experience in conducting such hand-sorting.